CN114966904A

CN114966904A - Nonlinear component for wavefront control based on graphene nonlinear super surface

Info

Publication number: CN114966904A
Application number: CN202210182218.8A
Authority: CN
Inventors: 徐亚东; 孙宝印; 朱杉; 金霞; 高雷; 周航
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2022-02-25
Filing date: 2022-02-25
Publication date: 2022-08-30
Also published as: WO2023159980A1

Abstract

The invention discloses a nonlinear component for wavefront control based on a graphene nonlinear super surface, which comprises a plurality of periodically distributed super-structure gratings, wherein each super-structure grating comprises a metal matrix, a plurality of periodically distributed grooves are formed in the metal matrix, dielectric layers are filled in the grooves, periodically distributed graphene strips cover the dielectric layers, and independent voltages are respectively applied to the graphene strips to control chemical potentials of the graphene strips so as to realize nonlinear phase gradient. The invention provides an improved diffraction law for nonlinear wave-front control based on a nonlinear phase gradient super surface of graphene in a terahertz domain, and the law can break through the limitation of NGSL to carry out nonlinear wave-front control; the chemical potential of the graphene is reasonably adjusted through the applied voltage, so that multifunctional control of nonlinear waves including retro-reflection, light beam control and the like is realized, and the design of a nonlinear component is realized.

Description

Nonlinear component for wavefront control based on graphene nonlinear super surface

Technical Field

The invention belongs to the technical field of optical systems, and particularly relates to a nonlinear component for wavefront control based on a graphene nonlinear super-surface.

Background

The super surface is composed of engineered planar super atoms in a two-dimensional geometry, and has attracted great interest in recent decades due to its strong ability to effectively control the amplitude, phase and polarization of electromagnetic waves. By designing sub-wavelength element atoms, many applications based on hypersurfaces have been proposed, including beam splitters, holographic imaging, superlenses, odd-even correlation diffraction and angular asymmetric diffraction, among others. Recently, the concept of a hypersurface has been extended to the nonlinear region. It provides a paradigm for studying nonlinear optics because stronger nonlinear optical responses can be created on more compact scales beyond the limitations of bulk nonlinear media.

Nonlinear hyper-surfaces have demonstrated typical nonlinear effects such as Second Harmonic Generation (SHG), Third Harmonic Generation (THG) and Four Wave Mixing (FWM). Local field enhancement is achieved in the super-surface paradigm by various resonance mechanisms, such as surface plasmons in plasmonic super-surfaces, Mie resonances in high dielectric constant super-surfaces, and Bound States (BICs) in continuous media. The interaction between light and nonlinear super-surfaces can be very strong even if the thickness of the object is very thin. Therefore, high conversion efficiency with low input intensity can be obtained without phase matching conditions. Although much effort has been devoted to nonlinear super-surfaces, most of the reported work to date has focused on improving the efficiency of nonlinear light generation, and little work has been done to study the wavefront control of the generated nonlinear light, i.e., to control the direction of the generated nonlinear waves. Using conventional methods, it is difficult to simultaneously generate nonlinear light and control its wavefront.

Therefore, in order to solve the above technical problems, it is necessary to provide a nonlinear device for performing wavefront control based on a graphene nonlinear super surface.

Disclosure of Invention

In view of this, the present invention provides a nonlinear device for wavefront control based on a graphene nonlinear super surface.

In order to achieve the above object, an embodiment of the present invention provides the following technical solutions:

the utility model provides a nonlinear components and parts based on graphite alkene nonlinear super surface carries out wave front control, nonlinear components and parts include a plurality of periodically distributed's super structure grating, super structure grating includes the metal base, is equipped with the recess of a plurality of periodically distributed on the metal base, and the recess intussuseption is filled with the dielectric layer, the dielectric layer coats and is stamped the graphite alkene area of periodically distributed, and graphite alkene takes and is applied independent voltage respectively in order to control the chemical potential in graphite alkene area, and then realizes nonlinear phase gradient.

In one embodiment, the metal matrix is made of gold, and the optical properties of gold are obtained by Drude model:

wherein f is _p 2069THz, γ 17.65 THz; the dielectric layer is made of PMMA, and the dielectric constant is 2.25.

In one embodiment, the super-structured grating comprises m periodically distributed grooves, a dielectric layer and a graphene strip, the width and the depth of each groove are w and h respectively, the distance between every two adjacent grooves is a, and the width of each graphene strip is w _g And w is _g W, the total length of the super-structured grating is p, p is ma, and the voltages applied to the m graphene strips are respectively V ₁ 、V ₂ 、...、V _m The phase difference between adjacent grooves is 2 pi/m.

In one embodiment, m is 2-5.

In one embodiment, the nonlinear element includes:

when m is 2, the phase difference between adjacent grooves is pi, and the chemical potentials of 2 graphene bands are 0.268eV and 0.160eV respectively;

when m is 3, the phase difference between adjacent grooves is 2 pi/3, and the chemical potentials of 3 graphene strips are 0.290eV, 0.218eV and 0.120eV respectively;

when m is 4, the phase difference between adjacent grooves is pi/2, and the chemical potentials of 4 graphene bands are 0.338eV, 0.266eV, 0.206eV and 0.120eV respectively;

when m is 5, the phase difference between adjacent grooves is 2 pi/5, and the chemical potentials of 5 graphene ribbons are 0.444eV, 0.340eV, 0.278eV, 0.212eV and 0.120eV, respectively.

In one embodiment, the nonlinear element includes:

when m is 2, the width w of the groove is 6 μm, the depth h of the groove is 7 μm, the distance a between two adjacent grooves is 10 μm, the total length of the super-structured grating is 20 μm, and the width w of the graphene strip is 10 μm _g ＝2μm；

When m is 3, the width w of the groove is 5 μm, the depth h of the groove is 7 μm, the distance a between two adjacent grooves is 6.67 μm, the total length of the super-structured grating is 20 μm, and the width w of the graphene strip is 3 _g ＝2μm；

When m is 4, the width w of the groove is 4 μm, the depth h of the groove is 7 μm, the distance a between two adjacent grooves is 5 μm, the total length of the super-structured grating is 20 μm, and the width w of the graphene strip is 4 μm _g ＝2μm；

When m is 5, the width w of the groove is 3 μm, the depth h of the groove is 7 μm, the distance a between two adjacent grooves is 4 μm, the total length of the super-structured grating is 20 μm, and the width w of the graphene strip is 3 μm _g ＝2μm。

In one embodiment, the incident light of the nonlinear component is FF light, and the reflected light is THG wave.

In one embodiment, the incident angle of the incident light is θ _i The reflection angle of the reflected light is theta _r And satisfies the following conditions:

wherein, the first and the second end of the pipe are connected with each other,

k

₀ 2 pi/λ, n is the diffraction order, G2 pi/p, q 3, phase gradient of

In one embodiment, the reflection angle is θ _r ＝arsin(λ _FF /3p)，λ _FF Is the wavelength of the incident light.

In one embodiment, the wavelength λ of the incident light _FF 60 μm, input intensity of 10KW/cm ² 。

In one embodiment, the incident angle θ of the incident light _i Less than critical angle theta _c The reflected light is diffracted into two diffraction orders, n being 0 and n being 1, and the incident angle theta of the incident light is _i Greater than critical angle theta _c The reflected light is diffracted into two diffraction orders, n 1 and n 2.

The invention has the following beneficial effects:

the invention provides an improved diffraction law for nonlinear wavefront control based on a nonlinear phase gradient super surface of graphene in a terahertz domain, and the law can break through the limitation of NGSL to perform nonlinear wavefront control;

the chemical potential of the graphene is reasonably adjusted through the applied voltage, so that multifunctional control of nonlinear waves including retro-reflection, light beam control and the like is realized, and the design of nonlinear components is realized.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a schematic diagram of a super-structured grating (unit cell) in a nonlinear device according to the present invention;

fig. 2a shows the optical characteristics (amplitude and phase) of the THG wave and the graphene chemical potential (E) when m is 2 _f ) A graph of (a);

fig. 2b is a magnetic field distribution diagram of the reflected THG wave when m is 2;

fig. 2c is an equal frequency graph of the incident angle and the reflection angle when m is 2;

FIG. 2d is a graph showing the relationship between the incident angle and the reflection angle when m is 2;

FIG. 3 shows the magnetic field (H) of THG wave at different incidence angles of FF light when m is 2 _y ) A simulation diagram;

fig. 4a shows the optical characteristics (amplitude and phase) of the THG wave and the graphene chemical potential (E) when m is 3 _f ) A graph of (a);

fig. 4b is a magnetic field distribution diagram of the reflected THG wave when m is 3;

fig. 4c is an equal frequency graph of the incident angle and the reflection angle when m is 3;

fig. 4d is a graph of the relationship between the incident angle and the reflection angle when m is 3;

FIG. 5 shows the magnetic field (H) of THG wave at different incident angles of FF light when m is 3 _y ) A simulation diagram;

fig. 6 is a graph of diffraction efficiency of THG light at two diffraction orders, where n is 0 and n is 2, when m is 2, 3, 4, and 5;

fig. 7 shows a magnetic field (H) of a THG wave with an FF light incident angle of ± 30 ° when m is 3 _y ) A simulation diagram;

fig. 8 shows magnetic fields (H) of THG waves having an FF light incident angle of 0 ° when m is 1, 2, and 3 _y ) And (5) simulating a diagram.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Inspired by the phase gradient super-Surface (PGMs) concept in linear optics, PGMs in nonlinear optics have been theoretically proposed and demonstrated by experiments, which provide a viable means for wavefront control of the generated nonlinear light. Specifically, Third Harmonic Generation (THG) is taken as an exampleThe designed nonlinear PGMs can not only generate THG, but also introduce abrupt phase shift for the THG

It can cover 2 pi completely. As an analogy to the linear case, the non-linear abrupt phase shift generates additional momentum

Resulting in a non-linear generalized snell's law (NGSL), namely:

wherein the content of the first and second substances,

k

₀ 2 pi/lambda is the wave vector of the fundamental frequency of incidence (FF) in free space,

the symmetry of the momentum space is broken and therefore, in order to keep momentum conservation, the THG must bend accordingly. For example, beam steering of nonlinear light is experimentally achieved in nonlinear super-surfaces, or asymmetric transmission in optically nonlinear super-surfaces is observed based on NGSL experiments. NGSL has become a cornerstone for arbitrary control of nonlinear wavefront, but it is only suitable for FF light with incidence angle below the critical angle defined by equation (1), and has theta _r At 90 °, i.e. θ _c ＝1-ξ/(3k ₀ ). Similar to the linear case, when the angle of incidence is above the critical angle, the NGSL will not be able to predict the angle of reflection or refraction of the nonlinear light. Therefore, there is a great limitation in the complete control of the nonlinear wavefront.

The present invention rechecks NGSL by designing and studying graphene-based nonlinear PGMs that can produce significant THG effects. Essentially, all designed nonlinear PGMs are periodic structures with super cells that repeat spatially along the interface. For such a structure, grating-based diffraction effects from the reciprocal lattice vector should be considered. Recent advances in linear PGMs indicate that higher order diffraction occurs when the incidence exceeds a critical threshold. Inspired by this development, we will show by studying reflective nonlinear PGMs that NGSL is indeed incorrect for FFs with incident angles exceeding the critical angle. The present invention will propose an improved diffraction law involving reciprocal lattice vectors that fully describes the diffraction behavior of the resulting nonlinear wave. This law of diffraction offers more opportunities to manipulate the propagation of nonlinear light and allows one to achieve many interesting effects. To illustrate, the present invention contemplates a nonlinear PGM-based retroreflector that can direct the nonlinear light generated back into the original direction of the incident FF light. Furthermore, taking advantage of the tunable nature of graphene ribbons, a tunable nonlinear PGM was designed and studied that can direct the reflection of generated THG in multiple directions by simply changing the periodic arrangement of the applied external voltage.

The invention discloses a nonlinear component which comprises a plurality of periodically distributed super-structure gratings. Referring to fig. 1, the super-structured grating includes a metal substrate 10, a plurality of periodically distributed grooves are formed in the metal substrate, a dielectric layer 20 is filled in the grooves, periodically distributed graphene strips 30 are covered on the dielectric layer 20, and independent voltages are respectively applied to the graphene strips to control chemical potentials of the graphene strips, so that a nonlinear phase gradient is realized.

Specifically, the material of the metal base 10 in this embodiment is gold (Au), and the optical characteristics thereof are obtained by Drude model:

wherein f is _p 2069THz, γ 17.65 THz. The material of the dielectric layer 20 is PMMA, and the dielectric constant is 2.25. To introduce a non-linear phase shift along the phase gradient super surface (PGM), different voltages are applied to the graphene ribbons 30.

Since the graphene strips 30 do not contact the metal grating, the chemical potentials of the m graphene strips can be changed by applying different voltages (V) ₁ 、V ₂ 、...、V _m ) To be controlled independently. The width and the depth of the groove are w and h respectively, and the width of the graphene strip is w _g <w. The distance between two adjacent grooves is a, so that the period of the super-structured grating is p ═ ma.

The grooves involved in the nonlinear super-surface can effectively enhance the interaction between light and the graphene band, and therefore the method has important significance for improving the conversion efficiency of the third harmonic and expanding the phase coverage range of the designed nonlinear phase gradient. In addition, the grooves can effectively avoid wave coupling between the super-structured gratings, so that higher-order diffraction can be easily observed in PGM. Note that in the considered terahertz (THz) operating frequency range, graphene is considered only as a nonlinear material in the present invention, since the third-order nonlinear coefficients of gold and PMMA are much smaller than graphene and therefore negligible. Linear conductivity (i.e. σ) of graphene _g ) Can be represented by a Drude model in which the relaxation time tau is set to 10 ^-13 s ^-1 . The designed graphene-based nonlinear super-surface can be fabricated by transferring the prepared single-layer graphene ribbons onto a PMMA-filled metal grating. Third Harmonic Generation (THG) is discussed as an example in the present invention.

Considering transverse magnetic wave (TM) polarized Fundamental Frequency (FF) light (i.e. magnetic field only in y-direction) that is typically incident to PGM from air, the graphene strips immediately generate THG signals due to photon interaction, and most of the nonlinear light generated will enter the grooves except a small amount of radiation entering the air. The THG then undergoes multiple reflections between the top and bottom of the groove, eventually reflecting back into the air. The THG phase radiating from each groove contains three components: (i) the accumulated phase of THG propagating within the groove, (ii) the abrupt phase caused by the graphene layer, (iii) the additional phase of multiple reflections between the top and bottom of the groove. Thus, the phase difference between two adjacent grooves (i.e., the phase difference between two adjacent grooves)

Mainly determined by graphene ribbons with different chemical potentials. When in use

When the abrupt phase shift completely covers 2 pi, continuous THG waves can be generated. T isThe abrupt phase shift required by the HG may be obtained by designing the appropriate chemical potential of each graphene strip by applying different voltages across the graphene strip, with V going from left to right in a super-structured grating ₁ 、V ₂ 、...、V _m And (4) showing. Upon introduction of an abrupt phase shift of the THG wave along the interface of the designed metasurface for an angle theta _i Incident FF light, reflection angle theta of THG _r Not determined by the NGSL equation (1)). But is determined by the following formula,

wherein G is 2 pi/p, n is diffraction order, and in THG, q is 3, and the phase gradient is

Formula (1) corresponds to the diffraction order in which n is 0 in formula (1). According to the formula (1), when theta is _i >θ _c When the THG wave is reflected, no diffraction channel is radiated to the free space; while according to equation (2), the THG wave can be coupled to higher orders and radiated outward as a propagating wave.

To verify the above theory, a nonlinear PGM with m 2 will be described as an example. Wherein the operating wavelength λ _FF 60 μm, 10 μm groove distance a, 7 μm groove depth h, 6 μm groove width w, graphene ribbon width w _g 2 μm. In this case, G ═ 3k ₀ ，ξ＝3k ₀ Meaning that the critical angle of the diffraction order where n is 0 is θ _c 0 °, to represent THG in the designed PGM, modeling was performed by COMSOL Multiphysics, with nonlinear graphene being modeled by nonlinear surface currents

Simulation, E _FF And E _TH Electric field, σ, of locally linear FF light and generated THG light ⁽³⁾ Is the third order nonlinear surface conductivity of graphene. THG radiation can be obtained by simulation in which the intensity of incident FF light is set to 10kW/cm if not stated ² 。

First considering THG from the designed PGM with the same graphene strip to reveal the relationship between the optical properties (including amplitude and phase) of the generated THG wave and the chemical potential of the graphene strip, the obtained result is shown in fig. 2a, where the incident wave is a TM polarized plane wave, when the applied chemical potential is E _f1 0.268eV (point B1) and E _f2 At 0.160eV (point a 1), the two cells acquire a nonlinear phase difference of magnitude pi, so that an abrupt phase shift (2 pi/m) is achieved at m 2. Fig. 2b shows the corresponding magnetic field distribution, clearly revealing the phase difference of the reflected THG waves in the two cells with which a non-linear PGM with m-2 can be designed.

To reveal the diffraction process, fig. 2c shows an isocratic plot based on equation (2). When the angle of incidence is below the critical angle, i.e. theta _i <0 °, the reflected THG wave is controlled by the NGSL, i.e., n ═ 0; when the angle of incidence exceeds the critical angle, i.e. theta _i >0 deg., the reflected THG wave will follow a diffraction order of n-2. Specular reflection (n ═ 1) always exists. Theoretically, the THG reflection angle of each diffraction order can be accurately calculated using equation (2), and the reflection angle of the THG wave is related to the incident angle as shown in fig. 2d, in which the simulation result (solid point) coincides with the calculation result (solid line) based on equation (2).

To verify the proposed law of diffraction, fig. 3 (a) to (f) show the numerically simulated magnetic field (H) of the THG wave of FF gaussian beam with different angles of incidence _y ) Mode(s). As described above for θ _i <At 0 °, the THG wave is mainly a diffraction order in which n is 0 and n is 1 at or below the critical angle, and (a) to (c) in fig. 3 are incident angles θ _i As a result of-15 °, -30 °, -60 °, in addition to the specular reflection, the anomalous reflection or radiation of the THG wave is in each case predominantly n-0 diffraction orders, corresponding to angles of reflection θ, respectively _r This result corresponds to the calculation in fig. 2d, 47.8 °, 30 °, 7.7 °. For theta _i >0 DEG, and at least the critical angle, and (d) to (f) in FIG. 3 are incident angles [ theta ] _i ＝15°，θ _i ＝30°，θ _i As a result of 60 °, the reflection angles of the THG waves are mainly n-2 diffraction orders, and the corresponding reflection angles are θ _r ＝-47.8°，θ _r ＝-30°，θ _r The result is consistent with the calculation in fig. 2d, which is-7.7 °. Furthermore, for specular reflection, the simulation results in FIG. 2d also fit well with the calculation results.

In principle, the diffraction law modified by equation (2) applies to the case where m is an arbitrary value, and the case where m is 2 to 5 is referred to and demonstrated in the present invention, the obtained results are almost the same, except that there is a difference in the diffraction efficiency of THG in each channel (which will be discussed later). Here, a case where m is 3 will be described as an example. To maintain consistency, the phase gradient of the THG wave is kept constant, i.e., ξ ═ 3k ₀ . The total length p of the metamaterial grating is 20 μm, the groove distance a is 6.67 μm, the groove depth h is 7 μm, the groove width w is 5 μm, and the width w of the graphene strip _g 2 μm. The phase difference between two adjacent units is 2 pi/3, and can also be realized by designing proper chemical potential. FIG. 4a shows the function relationship between the amplitude and phase of the reflected THG wave and the chemical potential of graphene when the FF light is normally incident, and the chemical potential E corresponding to the phase difference of 2 pi/3 is realized _f1 0.290eV (point C2), E _f2 0.218eV (point B2) and E _f3 0.120eV (point a 2). Fig. 4b shows the corresponding magnetic field distribution, clearly revealing the phase difference of the reflected THG waves in the three cells.

Because xi is 3k ₀ And the critical angle of the super surface is theta when m is 3 _c 0 deg.. For theta _i <0 °, the reflected THG wave will be diffracted into two diffraction orders, i.e. n-0 and n-1 in fig. 4 c; for theta _i >At 0 °, the reflected THG wave is diffracted into two diffraction orders, i.e., n-1 and n-2 in fig. 4 c. As can be seen from comparing fig. 2c and fig. 4c, the diffraction rules of m-2 and m-3 are the same, and therefore, the relationship between the reflection angle and the incident angle of the THG wave is the same in both cases of m-2 and m-3, as shown in fig. 2d and fig. 4 d.

In order to verify diffraction when m is 3, (a) to (f) in fig. 5 show numerical simulation magnetic fields (H) of THG waves of FF gaussian beams having different incident angles when m is 3 _y ) Mode(s). For theta _i <At 0 °, the THG wave is mainly a diffraction order in which n is 0 and n is 1 at or below the critical angle, and (a) to (c) in fig. 5 are incident angles θ _i Results at-15 °, -30 °, -60 °, reflectedThe THG wave is diffracted by n-0 and n-1 diffraction orders, and the corresponding reflection angles are respectively theta _r 47.8 °, 30 °, 7.7 °, which result corresponds to the calculation in fig. 4 d. For theta _i >0 DEG, and at least the critical angle, and (d) to (f) in FIG. 5 are incident angles [ theta ] _i ＝15°，θ _i ＝30°，θ _i As a result of 60 °, the reflected THG wave is diffracted by n-1 and n-2 diffraction orders, with corresponding reflection angles θ _r ＝-47.8°，θ _r ＝-30°，θ _r The result is consistent with the calculation in fig. 4d, which is-7.7 °. Furthermore, for specular reflection, the simulation results in FIG. 4d also fit well with the calculation results.

Furthermore, the diffraction efficiency is m-dependent for the diffraction efficiency (i.e. conversion efficiency) in each channel, especially for the n-0 and n-2 diffraction orders. Diffraction efficiency is defined as C _eff ＝P _TH /P _FF In which P is _FF Is the input power of the incident wave, P _TH Is the output power of the reflected THG wave for each diffraction channel. In fig. 6, when (a) to (d) are

m

2, 3, 4, and 5, respectively, the diffraction efficiencies of THG light in two diffraction orders, n 0 and n 2, are respectively, and the input intensity of incident FF light is 10KW/cm in each case ² . Where m-2 is a special case because the nonlinear PGM is designed to have mirror plane symmetry, and therefore, the diffraction response of THG light has angular symmetry for full incidence (see fig. 6 (a)). For m33, this mirror symmetry is broken, resulting in an angularly asymmetric response (see (b) - (d) in fig. 6). In the simulation and calculation, for m 4, the groove distance a is 5 μm, the groove depth h is 7 μm, the groove width w is 4 μm, and the width w of the graphene ribbon is 4 μm _g 2 μm, the chemical potentials of the graphene ribbons are each E in order to obtain the desired nonlinear phase difference between adjacent units pi/2 _f1 ＝0.338eV、E _f2 ＝0.266eV、E _f3 0.206eV and E _f4 0.120 eV. For m 5, the groove distance a 4 μm, the groove depth h 7 μm, the groove width w 3 μm, the width w of the graphene ribbon _g 2 μm, the chemical potentials of the graphene strips are respectively E in order to obtain the desired nonlinear phase difference between adjacent units of 2 pi/5 _f1 ＝0.444eV、E _f2 ＝0.340eV、E _f3 ＝0.278eV、E _f4 0.212eV and E _f5 ＝0.120eV。

As m increases, the conversion efficiency of n-2 diffraction orders decreases gradually and eventually becomes smaller. The physical mechanism of this asymmetric THG conversion is mainly due to multiple reflection effects in the higher order diffraction. Note that n-0 is the lowest diffraction order, and n-2 is higher. Similar to the results in linear PGM, THG undergoes one round trip within the groove in the n-0 diffraction order, while for higher order diffraction (i.e., n-2 diffraction orders), THG undergoes multiple reflections and round trips within the groove (L-m-n + 1). This means that the round trip is m-dependent, in particular L ═ 1(m ═ 2) and L ═ 2(m ═ 3). More round-trips in the higher order diffraction result in more energy dissipation due to ohmic losses of gold and graphene. Thus, for m-2, the diffraction response is symmetric because n-0 and n-2 round trips are the same. For m-3, the round trip is L-1 (n-0) and L-2 (n-3), respectively; then, the THG efficiency of incident waves above the critical angle is less than incident waves below the critical angle. Furthermore, as m increases, the degree of asymmetric response becomes more severe.

The diffraction laws and THG efficiency response at each diffraction order proposed by the present invention provide a way to design a nonlinear device with a fan-like function. In particular, in PGM design, the graphene used is electrically tunable, and the design of tunable devices is greatly facilitated only by changing the chemical potential of the graphene. For illustration, the present invention has designed a non-linear retroreflector, which means that the reflected THG wave can be redirected back to its original direction, i.e., θ _r ＝-θ _i . The function of nonlinear retroreflection is demonstrated by m 2. The geometric parameters of the designed nonlinear retroreflector are set as a 10 μm, w 6 μm and w _g ＝2μm，p＝λ _TH 20 μm, nonlinear phase gradient ξ 3k ₀ . According to the formula (2), when the incident wave is lambda _FF When the angle of 60 μm is ± 30 °, nonlinear retroreflection can be realized. To obtain non-linear retroreflection, the chemical potential of the graphene ribbons was chosen as E _f1 0.268eV and E _f2 0.160eV to produce a nonlinear phase difference of pi. To reveal non-linear retroreflectors of this designPerformance, the simulated reflection fields of the THG wave are shown in fig. 7 (a) and (b), respectively. Clearly indicating when theta _i At-30 deg. the reflection angle of the THG wave is theta _r 30 ° (see fig. 7 (a)). Also for theta _i 30 DEG, the reflection angle of THG wave is theta _r -30 ° (see fig. 7 (b)).

In addition, by utilizing the electrically tunable characteristic of graphene, a tunable device can be designed, and the generated THG can be controlled in multiple directions only by changing the chemical potential of graphene. Based on the formula (2), the outgoing direction of the generated THG wave with respect to the incident FF light is theta _r ＝arsin(λ _FF And/3 p). By adjusting the size of p, the emission direction of the generated THG can be controlled. Since the phase coverage 2 pi in the entire super-structured grating is implemented by m cells, in the conventional design, once the configuration of PGM is fixed, it is difficult to change the size of the super-structured grating. However, in such a design using graphene, it becomes very convenient to simply align and combine different voltages applied to the graphene strips.

For example, the geometric parameters are selected to be a 10 μm, h 7 μm, w 6 μm and w _g 2 μm. When the same voltage is applied to all graphene strips (chemical potential of graphene strip is E) _f 0.100eV), there is no phase gradient along the metasurface. The THG wave will then be reflected by following Snell's law, i.e. θ _r ＝θ _i At 0 °, as shown in fig. 8 (a), the applied voltage has a characteristic of "AAAAAA" arrangement. When two different voltages (E) are periodically applied to the graphene strip _f1 0.268eV and E _f2 0.160eV) to achieve a phase gradient ξ of 3k ₀ When p is 20 μm, the reflection angle of the THG wave is θ _r As shown in fig. 8 (b), the arrangement of the applied voltages becomes "ABABAB" in this case. When three different voltages are periodically applied to the graphene strip, i.e. E _f1 ＝0.270eV、E _f2 0.202eV and E _f3 0.100eV, the nonlinear phase difference of adjacent units is 2 pi/3, and the phase gradient is xi 2k ₀ P 3a 30 μm, and the reflection angle of the THG wave is θ _r 41.8 °, as shown in fig. 8 (c), in this case, the arrangement of the applied voltagesIs "ABCABCABC". In this way a tunable device for wavefront control is obtained. Furthermore, as m increases, the pixels of PGM become very small as the width a enters the deep sub-wavelength scale. By applying voltage permutations and combinations in nonlinear metasurfaces, nonlinear wavefront control can be flexibly performed.

According to the technical scheme, the invention has the following advantages:

the chemical potential of the graphene is reasonably adjusted through the applied voltage, so that multifunctional control of nonlinear waves including retro-reflection, light beam control and the like is realized, and the design of a nonlinear component is realized.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. The utility model provides a nonlinear components and parts based on graphite alkene nonlinear super surface carries out wave front control, its characterized in that, nonlinear components and parts include a plurality of periodically distributed's super structure grating, super structure grating includes the metallic matrix, is equipped with the recess of a plurality of periodically distributed on the metallic matrix, and the recess intussuseption is filled with the dielectric layer, the dielectric layer coats and is stamped the graphite alkene area of periodically distributed, and graphite alkene area is gone up and is applied independent voltage respectively in order to control the chemical potential in graphite alkene area, and then realizes nonlinear phase gradient.

2. The nonlinear component as recited in claim 1, wherein the metal matrix is made of gold, and the optical properties of gold are obtained by Drude model:

3. The nonlinear component as claimed in claim 1, wherein the meta-grating comprises m periodically distributed grooves, a dielectric layer and a graphene strip, the width and depth of each groove are w and h respectively, the distance between two adjacent grooves is a, and the width of the graphene strip is w _g And w is _g W, the total length of the super-structured grating is p, p is ma, and the voltages applied to the m graphene strips are respectively V ₁ 、V ₂ 、...、V _m The phase difference between adjacent grooves is 2 pi/m.

4. The nonlinear component as claimed in claim 3, wherein m is 2-5.

5. A non-linear component as claimed in claim 4, wherein:

6. A non-linear component as claimed in claim 5, wherein the non-linear component comprises:

7. The nonlinear component as claimed in claim 4, wherein incident light of the nonlinear component is FF light, and reflected light is THG wave.

8. The nonlinear component as claimed in claim 7, wherein the incident angle of the incident light is θ _i The reflection angle of the reflected light is theta _r And satisfies the following conditions:

wherein the content of the first and second substances,

k ₀ 2 pi/lambda, n is the diffraction order, G2 pi/p, q 3, and the phase gradient is

9. The nonlinear component as claimed in claim 8, wherein the reflection angle is θ _r ＝arsin(λ _FF /3p)，λ _FF Is the wavelength of the incident light.

10. A non-linear component as claimed in claim 7, characterized in that the wavelength λ of the incident light is _FF 60 μm, input intensity of 10KW/cm ² 。

11. The nonlinear component as claimed in claim 8, wherein the incident angle θ of the incident light _i Less than critical angle theta _c The reflected light is diffracted into two diffraction orders, n is 0 and n is 1, and the incident angle theta of the incident light is _i Greater than critical angle theta _c The reflected light is diffracted into two diffraction orders, n 1 and n 2.